Osteoporosis, degenerative joint disease and primary muscle atrophy are three age-related disorders of the musculoskeletal system. Osteoporosis affects 90% of women over 75 years, osteoarthritis afflicts 80%, and muscle atrophy is progressive with age. Physical conditioning retards bone loss, stabilizes deteriorated joints and prevents muscle atrophy. The most efficient stimulus to produce these effects is therapy utilizing submaximal eccentric muscle contraction. Exercise of this type generates an equivalent training effect with less energy expenditure and less cardiovascular stress. We feel investigation of these effects is warranted. There are presently no user operated devices available to study exercise in which the resistance in the lifting phase of the cycle can be different from the resistance during the lowering phase. Therefore, in order to study the unique properties of eccentric muscle contractions, it will first be necessary to have the proper testing equipment available. We are therefore soliciting a SBIR Phase I grant to the development of a mechanism with which eccentric muscle conditioning can be performed. The application of the principles learned from this project could increase function and activity for post-surgical patients, neurologically impaired individuals as well as older Americans.